retarded

i saw the word "attarde'" but i was told not to use it. i guess it's insulting. is "de'bile mental" the proper way to refer to a person who is retarded? if u want to say a person is retarded, do u use "arrie're'"? and is de'bile also used colloquially to mean "idiot" as in "quel de'bile"?

i use the reverso dictionary. i'm quite sure i got attarde' there but i asked a french woman if it was right and she told me never to use it. i'm surprised the dictionary is so wrong on this cuz i find it very reliable. it would even use "debile" w qualifying words like "mildly" which made it appear it's proper usage.